Question $5$: Suqqested Time $-10$ minutes $($CO$2/$PO$2/$C$3-5\%)$

An engine production line has $3$ milling machines with reliabilities of $0\mathrm{.}98,0\mathrm{.}96,$ and $0\mathrm{.}93,$ respectively. The production line was designed in a way that if one of the machines is malfunctions, the line will shut down. To increase the line's reliability, En$.$ Abu who is the maintenance engineer has considered two designs options. Option $1$ is to add an identical backup line and Option $2$ is to provide a backup for each machine. The reliability of machine $1$ is similar, while machines $2$ and $3$ are $0\mathrm{.}97$ and $0\mathrm{.}92,$ respectively.

Choose the best plan that will provide higher reliability. Next, explain the reason of two reliabilities is not the same.